This application claims the priority of Japanese patent document 10 029501, filed Feb. 12, 1998, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a control device for for use in a motor vehicle generator and, more specifically, to a control device for an electric generator which is suitable for being driven by an internal combustion engine having a large load variation.
Automobiles are provided with a battery which is designed to supply an electric power to electric loads such as lamps, actuators and the like and an electric generator for charging the battery. Ordinarily, the generator of this sort is an inductor type AC generator in which a field winding is excited and is rotated by the driving torque caused by an engine. A battery charging voltage generated via the excitation of the field winding is controlled through a voltage regulator so as to maintain the same at a predetermined value.
However, when the electric load increases (such as by turning on the lamp switches and the like), it is in general necessary to correspondingly increase the amount of electric power to be generated; therefore, the current flowing through the field winding of the generator is also controlled increase rapidly. As a result, since the work load of the generator increases, the torque generated by the generator is also increased. Accordingly, the balance between the torque generated by the generator and the driving torque generated by the engine is lost, the engine rpm drops correspondingly to the increased fraction of the torque generated by the generator, and in the worst case the engine may stall. Particularly, during an idling condition in which the engine is controlled so as to maintain a predetermined rpm, while keeping a balance between the engine drive torque and the torque and the torque generated through the generator caused by auxiliaries including the generator, it is undesirable to experience a rapid torque variation which exceeds the response speed of the rotation control.
In order to suppress such phenomenon, a so called gradual excitation control has been proposed which suppresses a rapid rise of the field current flowing through the field winding, when a large electric load is suddenly applied to the generator. In this manner, rapid variations of the torque generated through the generator with regard to that of the engine can be prevented.
In the above gradual excitation control, the current to be generated is gradually increased and the generator cannot supply a necessary current immediately in response to an electric load change; therefore, the battery supplies a current to the load to supplement the shortage. If the current thus drawn out from the battery is large, a battery voltage drop is caused. Such drop is experienced especially at night when a head light, back lamps for a meter panel and an in-cabin lighting are used. In that case, when cyclical loads such as a hazard light and a wiper are turned on, resulting brightness fluctuation due to the battery voltage variation can be uncomfortable to the driver.
A counter measure for preventing such battery voltage drop caused by the gradual excitation control is disclosed in Japanese patent document JP-A-6-54464 (1994). There, at the moment when a load is turned on and prior to activating the gradual excitation control, the exciting current flowing through the field winding is once increased immediately to a predetermined amount, so as to supply to the electric load a generated current (for example amount 10 A) a level which causes no problem in connection with a rapid increase of the torque generated through the generator with regard to the engine torque. Thereafter, the gradual excitation control is started and the output current of the generator is gradually increased, so that the battery voltage drop immediately after the loading can be decreased.
In the above mentioned prior art JP-A-6-54464 (1994), at the moment when switching in an electric load (but prior to starting the gradual excitation control), the excitation current is immediately increased by a predetermined amount. However, when determining the increased amount of the excitation current, the characteristics of the concerned generator were not taken into account. For this reason, if a common control device is used for respective generators having different power generation capacities, an output current which is large relative to the predetermined excitation current (in other words, a large amplification rate by the generator) is obtained for a generator having a large power generation capacity. Therefore, after having increased the generation current (for example by about 10 A), by increasing the excitation current once by a predetermined amount at the moment when an electric load is switched in, the control device operates so as to gradually increase the generation current through the gradual excitation control. However, for a generator having a small power generation capacity, the output current is small relative to the excitation current. Thus, when the excitation current is increased once by the same predetermined amount as the generator having a large power generation capacity, the immediately generation current response is relatively small (for example about 2 A) in comparison with that of the generator having a large power generation capacity.
An object of the present invention is to provide a control device for an electric generator in a vehicle which reduces the battery voltage drop even for a generator having a small power generation capacity to a level comparable with that for a generator having a large power generation capacity.
An object of the present invention is achieved by a control device for a motor vehicle generator of the type which is driven by an engine for charging a battery by rectification of its output, and has a voltage regulator for maintaining the charging voltage of the battery at a constant level, and a gradual excitation control device which gradually increases the generation current of the generator after an electric load is switched in. According to the invention, the amount of increase of control current of a power switch for controlling the excitation current of the generator at a moment immediately after switching in the electric load, but prior to the activation of the gradual excitation control means, is adjusted depending on power generation conditions of the generator.
Preferably, according to the present invention, the amount of increase of the control current of the power switch for controlling the excitation current of the generator is adjusted depending on the generation current of the generator in such a manner that when the generation current is large, the amount of the increase is enlarged, and when the generation current is small, the amount of increase is reduced.
Further preferably, according to the present invention, the amount of increase of the control current of the power switch for controlling the excitation current is adjusted to a value proportionate to the excitation current prior to switching in the electric load.
Still a further object of the present invention is achieved by a control device for a motor vehicle electric generator of the type described above, which has a circuit the generates an integration output of a value determined by adding a deviation signal output (obtained by comparing the output voltage of the battery or the generator with a predetermined set voltage) to a predetermined amount of voltage, and selects the lower of the deviation signal output and the integration output as a control signal for controlling the excitation current of the generator. The predetermined amount of voltage to be added to the deviation signal output is controlled to be proportional to the value of the deviation signal output.
The object of the present invention is achieved by a control device for a motor vehicle electric generator comprising a field winding which is driven by rotation of an engine and generates rotating magnetic field; an armature winding which receives the rotating magnetic field, generates current and charges a battery via a rectifier; a voltage detecting circuit which detects the voltage of the battery or of the rectifier; a setting voltage circuit which generates a reference voltage; a deviation signal output circuit which receives the output voltage of the voltage detecting circuit and the reference voltage of the setting voltage circuit as the inputs and outputs a deviation signal; an adder circuit which adds a voltage proportional to the output voltage from the deviation signal output circuit to the output voltage of the deviation signal output circuit; a sawtooth wave generating circuit which outputs a voltage having rising and falling waveform within a predetermined voltage region at a preset cycle; an integration circuit which responds to the output of the adder circuit with a time constant which is longer than that of the field winding; and a comparator which receives as a first input thereof the lower of the deviation signal and the output voltage of the integration circuit, and as a second input thereof the output voltage of the sawtooth wave generating circuit as its inputs, wherein the current supplied to the field winding is controlled by the output from the comparator.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.